Radioactive sources are used in the art for both diagnosis and treatment of patients, especially human patients Such radioactive sources for such use are normally contained in a "safe" which avoids radiation hazard to technicians or physicians using the radioactive source in a diagnostic or treatment application. However, when the source is to be deployed, for example, in a human patient, the radioactive source must be driven from the safe to the place of diagnosis or treatment in the patient. To this end, the radioactive source is normally contained in a capsule and that capsule is attached to a drive member, most usually a flexible cable, so that the capsule and cable may be driven through a tubular guide from the safe to the point of disposition in the patient. This technique is referred to in the art as brachy therapy, e.g. intracavitary, intralumenal and interstitial radiotherapy, and this technique has become of increased importance in the treatment of certain diseases, especially cancer, in that the radiotherapy can be administered to very localized human body areas, as opposed to broad beam radiotherapy. To achieve this localized radiotherapy, the radioactive source must be placed in close proximity to the tissue being treated, since the radioactive source emits low levels of radiation at a distance from the locus of therapy and only high levels at the locus of therapy (the inverse square of the distance law). Thus, the application of the radiotherapy is normally achieved by guiding a radioactive source through at least one tubular guide until that source reaches the site of the tissue to be treated, e.g. cancerous tissue. A regiment of radiation is then administered according to a program defined for the particular cancerous tissue, and the therapy is, usually, periodically repeated until effective control of the cancerous tissue is achieved
Since repeated treatments may be required, it is important that the technician or physician administering the treatment not be in close proximity to the patient during treatment, since the radioactive source, while emitting low levels of radiation at a distance from the source, emits high levels of radiation near the source, and over a period of time and with numerous patients this can result in dangerous total radiation to the technician or physician. To avoid such radiation hazard to the technician or physician, apparatus has been developed so that the radioactive source is not moved from the safe until the apparatus is fully in place on the patient and the technician or physician is not in close proximity to the patient during treatment, e.g. in a separate room. Such apparatus is known in the art as remote after loading apparatus for brachy therapy, e.g. intracavitary, intralumenal and interstitial radiotherapy. For example, when using such apparatus, a technician interstitially places a positioning member, e.g. a needle or canula at the site where radiotherapy is to be effected. This positioning member is then attached to one end of a tubular guide, and the tubular guide is attached at the other end thereof to a connection head of the remote after loading apparatus. After such positioning and connections are made, a technician, from a remote location, e.g. another room, can cause the apparatus to drive a cable with the radioactive source contained in a capsule attached to the cable from the safe, through the remote after loading apparatus, the tubular guide and into the positioning member for radiotherapy. Thus, the technician will not be in close proximity to the patient while the radioactive source is out of the safe and while administering the therapy.
While apparatus of the above nature has been used for some time, a particular problem in connection therewith has been the ability of the capsule containing the radioactive source to be driven through the apparatus, especially the tubular guide, when that tubular guide is disposed in a tortuous path. The capsule, for safety reasons, must ensure that the radioactive source or sources contained therein are not dislodged from the capsule either while in the after loading apparatus or while passing through the tubular guide or while in the patient. To this end, the capsules are made of metal, and the radioactive source or sources are sealed in the metal capsule, usually by welding, to ensure that no dislodging of the radioactive sources will take place. Since the capsule is made of metal, the capsule is rigid, and when the capsule encounters a tortuous turn in the tubular guide, or other parts of the apparatus or in the patient, the capsule may not be able to traverse that tortuous turn and becomes lodged. As can be appreciated from the foregoing, it is therefore important that the length of the rigid capsule be as short as possible. Typically, the internal diameter of the tubular guide will only be about 1.5 millimeters or less and, consequently, the diameter of the capsule must be about 1.5 millimeters or less, usually about 1.1 millimeters. The capsules most often contain one or a plurality of radioactive sources, e.g. 4, 5, 6, 7, 8 or even 10 or more, and the length of the capsule is correspondingly increased with the number of sources. A typical capsule, containing seven radioactive sources, will have an overall length of approximately 7.2 millimeters. When a capsule of that length encounters a tortuous turn, e.g. in the tubular guide, the chances of the capsule binding in that turn significantly increases.
As can be appreciated from the foregoing, even small deviations in the length of the capsule significantly affect the ability of the capsule to traverse such tortuous turns.
In the usual and known method of manufacturing source capsules, a flexible transport cable is attached to the back end of the capsule. The front end of the capsule is open so that the required radioactive source or numbers of sources may be placed into the capsule. Thereafter, the front end of the capsule is sealed by inserting a rounded plug into the front end of the capsule, and that plug is then attached to the capsule, usually by welding. However, in such a welding operation, the plug must be held in position for welding by a holder having a pair of tongs or grippers with the result that the plug must have a certain minimum length in order to be securely held by such holder during the welding operation. In addition, the attachment, e.g. weld, is tested by a strong axial pull on the plug and the apparatus for gripping the plug for such pull test requires a plug of substantial relative length, e.g. about a minimum of 1.35 millimeters. As can be appreciated, this pull test is necessary in order to insure that the plug is well attached to the capsule, since if the plug dislodged from the capsule and allowed the source or sources to be lost in the apparatus, or much worse in the patient, disastrous results would ensue Consequently, the overall length of the capsule, with the plug attached, is increased beyond that necessary for the capsule containing the radioactive sources, and this increased length increases the chances of the capsule binding in the tubular guide or other parts of the apparatus during an attempted traverse of a tortuous turn.
As can, therefore, be appreciated, it would be a substantial advantage to the art to provide a capsule which can contain the same number of radioactive sources as known capsules, but which capsule is of a significantly shorter length than the known capsules